Wednesday, January 4, 2012
For the most part, spiders are harmless and generally beneficial. Spiders are seldom aggressive and bite only when threatened or injured. Few spiders ever bite people, and the venom of most species is harmless to humans. However, bites from the brown recluse (also known as the Recluse or Fiddle-Back) and the black widow can be quite dangerous. Please keep in mind, the more you understand any pest, the easier it will be to control.
Spiders are the largest group of arachnids. There are more than 35,000 named species worldwide, including about 3,000 in
North America, but probably most spider species are still awaiting identification. These predators live almost everywhere: on the ground, under rocks, inside and underneath playground equipment, among grasses, on plants, in tree branches, in underground caves and even on the water – depending on the species. Spiders frequently stray into dwellings and other structures, or may be accidentally introduced on firewood, laundry that has been hung out to dry, or on flowers, etc. Spiders will also sneak into our homes in boxes, clothing or furniture, through window areas and any crack or crevice that allows them entry. Web-building spiders often construct webs near lights because insect prey may be attracted at night by the lights and by air currents.
Spiders are easily recognized by the 4 pairs of seven segmented legs and (like all arachnids) have a cephalothorax and abdomen. But unlike scorpions, mites and daddy-long-legs, the cephalothorax and abdomen of the spider are separated by a visible waist or pedicel. The top of the cephalothorax is protected by a shield-like covering called the carapace.
Most species have 8 simple eyes, although some have less and a few species have none. Often the number and arrangement of eyes are important in identifying the different families. Below the eyes are 2 small jaws (or chelicerae) that end in fangs. Venom is produced in glands and empties through a duct in the fangs. This venom is used to paralyze or kill prey. Then the spider crushes the victim by rubbing the chelicerae against each other and against the enlarged bases of the pedipalps, located before the first legs. There are usually 6 finger-like silk glands (spinnerets) located beneath the abdomen, just in front of the anus.
Not all spiders spin webs. Some live in burrows, which they line with silk, while others have no retreat at all. All young spiders and some adult males release long silken strands, which they use like a parachute to ride on wind currents to other areas - a process is called ‘ballooning’.
Most spiders lay their eggs in silken egg sacs that are placed in the web, attached to leaves or twigs, or carried around by the spider until the eggs hatch. Spiderlings (as the young are sometimes called) resemble adults and are often cannibalistic. All spiders are predators and most feed on insects, although a few large species prey on small vertebrate animals.
This is the Brown Recluse Spider
Brown Recluse on a quarter
Black Widow Spider
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